Joseph I. Friedman

CNTNAP2 gene dosage variation is associated with schizophrenia and epilepsy

A homozygous mutation of the CNTNAP2 gene has been associated with a syndrome of focal epilepsy, mental retardation, language regression and other neuropsychiatric problems in children of the Old Order Amish community. Here we report genomic rearrangements resulting in haploinsufficiency of the CNTNAP2 gene in association with epilepsy and schizophrenia. Genomic deletions of varying sizes affecting the CNTNAP2 gene were identified in three non-related Caucasian patients. In contrast, we did not observe any dosage variation for this gene in 512 healthy controls. Moreover, this genomic region has not been identified as showing large-scale copy number variation. Our data thus confirm an association of CNTNAP2 to epilepsy outside the Old Order Amish population and suggest that dosage alteration of this gene may lead to a complex phenotype of schizophrenia, epilepsy and cognitive impairment.

Diffusion Tensor Imaging Findings in First-Episode and Chronic Schizophrenia Patients

OBJECTIVE Comparisons of diffusion tensor imaging (DTI) data between first-episode and chronic schizophrenia patients assessed in different studies have led to the suggestion that the decreased fractional anisotropy observed in chronic schizophrenia patients is less pronounced in first-episode patients. However, such comparisons of imaging data generated across studies are susceptible to numerous confounders, which may limit the interpretation of any differences. In order to address these issues and determine whether the DTI abnormalities of chronic schizophrenia are present at illness onset, the authors conducted a DTI investigation of the largest cohort of first-episode schizophrenia patients yet reported in conjunction with a group of chronic schizophrenia patients and healthy subjects for comparison. METHOD Fractional anisotropy data generated by diffusion tensor imaging with a 3-T Siemens Allegra head-dedicated MRI system were compared between 40 first-episode schizophrenia patients and 39 age- and gender-matched healthy comparison subjects and between 40 chronic schizophrenia patients and 40 age- and gender-matched healthy comparison subjects. The following regions of interest were assessed: forceps minor (bilaterally), forceps major (bilaterally), inferior longitudinal fasciculus (bilaterally), and the genu and splenium of the corpus callosum. RESULTS In most regions, chronic schizophrenia patients showed significant or trend-level lower fractional anisotropy than healthy comparison subjects, whereas the first-episode schizophrenia patients showed only trend-level lower fractional anisotropy in the inferior longitudinal fasciculus. CONCLUSIONS The cross-sectional data reported here suggest less widespread changes in white matter at illness onset in schizophrenia which progress in more chronic states. More definitive conclusions will require follow-up imaging of first-episode schizophrenia patients.

A double blind placebo controlled trial of donepezil adjunctive treatment to risperidone for the cognitive impairment of schizophrenia

BACKGROUND Despite the beneficial effects of atypical antipsychotics on cognition, these improvements will not return most schizophrenic patients to normative standards of cognitive functioning. Therefore, other treatments need to be considered. Subtle changes in cholinergic function in schizophrenic patients provide the rationale to test the effectiveness of cholinesterase inhibitors in treating cognitive impairment in schizophrenia. METHODS Given this, a 12-week, double-blind, placebo-controlled trial of donepezil (5 mg and 10 mg) as adjunctive treatment to risperidone was conducted in a total of 36 schizophrenic patients. RESULTS Neither the 5-mg nor 10-mg dose of donepezil produced significant improvements in any cognitive measure compared with placebo. CONCLUSIONS It is possible that nicotinic receptor desensitization produced by chronic tobacco use in these patients rendered their nicotinic receptors refractory to the effects of increased agonist activity produced by donepezil. An alternative treatment is the allosterically potentiating ligands, which enhance the activity of (sensitize) nicotinic receptors in the presence of acetylcholine.

Cholinergic targets for cognitive enhancement in schizophrenia: focus on cholinesterase inhibitors and muscarinic agonists

RationaleAlterations in the central cholinergic system of patients with schizophrenia such as reduced numbers of muscarinic and nicotinic receptors in the cortex and hippocampus may contribute to the cognitive impairment of schizophrenia. Therefore, pharmacological treatments that enhance central cholinergic function may be useful as cognitive enhancers in schizophrenia.MethodsSearches were conducted for articles which investigated alterations of central cholinergic systems in patients with schizophrenia. Additional searches were conducted for animal and human trials of potential cognitive enhancing compounds that target the cholinergic system and any preliminary trials conducted with schizophrenic patients.ResultsCurrently available treatments which are potentially suitable for this purpose include acetylcholinesterase inhibitors, muscarinic agonists, nicotinic agonists, and allosteric potentiators of nicotinic receptor function. Although some open label studies demonstrate modest cognitive improvements of schizophrenic patients treated with donepezil, data from a blinded, placebo controlled study demonstrate no effect. Data from a controlled trial of galantamine, a combined acetylcholinesterase inhibitor and allosteric potentiator of the nicotinic receptor, indicates that this may be an effective alternative. In addition, some preclinical data indicates that selective M1 muscarinic agonists under development may have potential as cognitive enhancers and antipsychotic treatments for schizophrenic patients.ConclusionsA cholinergic approach to ameliorating the cognitive dysfunction of schizophrenia appears viable. There is some preliminary data to support the efficacy of combined acetylcholinesterase inhibitors and allosteric potentiators of the nicotinic receptor, whereas future trials are awaited for more specific muscarinic agonists currently under development.

Strong synaptic transmission impact by copy number variations in schizophrenia

Schizophrenia is a psychiatric disorder with onset in late adolescence and unclear etiology characterized by both positive and negative symptoms, as well as cognitive deficits. To identify copy number variations (CNVs) that increase the risk of schizophrenia, we performed a whole-genome CNV analysis on a cohort of 977 schizophrenia cases and 2,000 healthy adults of European ancestry who were genotyped with 1.7 million probes. Positive findings were evaluated in an independent cohort of 758 schizophrenia cases and 1,485 controls. The Gene Ontology synaptic transmission family of genes was notably enriched for CNVs in the cases (P = 1.5 × 10−7). Among these, CACNA1B and DOC2A, both calcium-signaling genes responsible for neuronal excitation, were deleted in 16 cases and duplicated in 10 cases, respectively. In addition, RET and RIT2, both ras-related genes important for neural crest development, were significantly affected by CNVs. RET deletion was exclusive to seven cases, and RIT2 deletions were overrepresented common variant CNVs in the schizophrenia cases. Our results suggest that novel variations involving the processes of synaptic transmission contribute to the genetic susceptibility of schizophrenia.

Pharmacologic strategies for augmenting cognitive performance in schizophrenia

There is recognition that the cognitive symptoms of schizophrenia have the most substantial impact on illness outcome. Domains of cognition reported to be significantly affected include serial learning, executive function, vigilance, and distractibility, to name a few. Dopamine activity at D1 receptors mediates many cognitive processes subserved by the prefrontal cortex (PFC), particularly working memory. The number of D1 receptors in the PFC is decreased in schizophrenics and is unaffected by chronic administration of typical neuroleptics. Therefore, medications that increase dopamine in the PFC, such as atypical neuroleptics, or that directly activate the D1 receptor may prove useful in the remediation of prefrontal-dependent cognitive deficits in schizophrenia. Decreased levels of cortical norepinephrine (NE) are associated with impaired learning and working memory in animal models, and can be reversed by drugs that restore NE activity. More specifically, alpha-2 adrenergic receptor agonists have been particularly effective in improving delayed response performance in young monkeys with localized 6-hydroxydopamine lesions in the PFC. Furthermore, human postmortem studies have demonstrated decreased NE in the frontal cortex of demented schizophrenic patients. Therefore, alpha-2 receptor agonists hold promise as drugs to improve cognitive performance on tasks dependent upon PFC function in schizophrenics. Finally, the finding that cortical choline acetyl transferase activity correlates with Clinical Dementia Rating scores in schizophrenic patients and that cholinomimetic drugs enhance cognition in healthy subjects suggests that cholinergic drugs may also treat cognitive symptoms in schizophrenia. Two potential types of cholinomimetics for use in schizophrenics are the acetylcholinesterase inhibitors and M1/M4 muscarinic agonists, both of which increase cortical cholinergic activity.

Diffusion tensor imaging in schizophrenia.

BACKGROUND Alignment of white matter axons as inferred from diffusion tensor imaging has indicated changes in schizophrenia in frontal and frontotemporal white matter. METHODS Diffusion tensor anisotropy and anatomical magnetic resonance images were acquired in 64 patients with schizophrenia and 55 normal volunteers. Anatomical images were acquired with a magnetization prepared rapid gradient echo sequence, and diffusion tensor images used a pulsed gradient spin-echo acquisition. Images were aligned and warped to a standard brain, and anisotropy in normal volunteers and patients was compared using significance probability mapping. RESULTS Patients showed widespread areas of reduced anisotropy, including the frontal white matter, the corpus callosum, and the frontal longitudinal fasciculus. CONCLUSIONS These findings, which are consistent with earlier reports of frontal decreases in anisotropy, demonstrate that the effects are most prominent in frontal and callosal areas and are particularly widespread in frontal white matter regions.

The role of norepinephrine in the pathophysiology of cognitive disorders: potential applications to the treatment of cognitive dysfunction in schizophrenia and Alzheimer's disease

The role of noradrenergic neurotransmission in normal cognitive functions has been extensively investigated, however, the involvement of noradrenergic functions in the cognitive impairment associated with schizophrenia and Alzheimers disease has not been as intensively considered. The limited ability of atypical antipsychotics to treat the cognitive impairment of schizophrenia, and cholinomimetics to treat the cognitive impairment of Alzheimers disease, may be related to the influence of a multiplicity of neurotransmitter abnormalities including noradrenergic dysfunction, which these treatments do not address. The evidence of noradrenergic dysfunction occurring concomitantly with dopamine dysfunction in schizophrenia and acetylcholine dysfunction in Alzheimers disease supports therapeutic approaches using noradrenergic drugs in combination with neuroleptics and cholinesterase inhibitors, respectively, to enhance the treatment of cognitive impairment. Given the results of animal and human studies, it appears that alpha-2A agonists may be the optimal choice for this purpose.

Guanfacine treatment of cognitive impairment in schizophrenia

Norepinephrine plays a significant role in the working memory functions of the prefrontal cortex by its actions at alpha-2a noradrenergic receptors. Guanfacine has demonstrated efficacy in reversing working memory deficits in non-human primate. In the present study the effect of guanfacine adjunctive treatment to neuroleptics on the cognitive performance of schizophrenic patients was investigated in a four week, placebo-controlled, double-blind, parallel design trial. The primary analyses revealed no significant differences between guanfacine and placebo treatment; however, exploratory non-parametric statistics revealed some significant and some trend differences between guanfacine and placebo on spatial working memory test performance and CPT reaction time in those subjects treated with atypical neuroleptics.

Brain metabolite abnormalities in the white matter of elderly schizophrenic subjects: implication for glial dysfunction

BACKGROUND Abnormalities in the white matter of the brain may occur in individuals with schizophrenia as well as with normal aging. Therefore, elderly schizophrenic patients may suffer further cognitive decline as they age. This study determined whether elderly schizophrenia participants, especially those with declined cognitive function (Clinical Dementia Rating score > 1), show white matter metabolite abnormalities on proton magnetic resonance spectroscopy and whether there are group differences in age-dependent changes in these brain metabolites. METHOD Twenty-three elderly schizophrenia and twenty-two comparison participants fulfilling study criteria were enrolled. Localized, short echo-time (1)H MRS at 4 Tesla was used to assess neurometabolite concentrations in several white matter regions. RESULTS Compared with healthy subjects, schizophrenia participants had lower N-acetyl compounds (-12.6%, p = .0008), lower myo-inositol (-16.4%, p = .026), and higher glutamate + glutamine (+28.7%, p = .0016) concentrations across brain regions. Schizophrenia participants with Clinical Dementia Rating >/= 1 showed the lowest NA in the frontal and temporal regions compared with control subjects. Interactions between age and schizophrenia status on total creatine and choline-containing compounds were observed; only schizophrenia participants showed age-related decreases of these metabolites in the right frontal region. CONCLUSIONS Decreased NA in these white matter brain regions likely reflects reduced neuronal content associated with decreased synapses and neuronal cell volumes. The elevated glutamate + glutamine, if reflecting elevated glutamate, could result from excess neuronal glutamate release or glial dysfunction in glutamate reuptake. The decreased myo-inositol in participants with schizophrenia suggests decreased glial content or dysfunctional glia, which might result from glutamate-mediated toxicity.